1. Field of the Invention
The present invention relates to a technique for printing through emission of ink droplets.
2. Description of the Related Art
In recent years, ink-jet printers, which emit ink onto a print medium from a print head, have come to enjoy widespread use as output devices for computers. While conventional ink-jet printers can only reproduce pixels in binary fashion (ON or OFF), multilevel printers that can reproduce pixels with three or more levels have been proposed more recently. Multilevel pixels can be reproduced, for example, by manipulating the size of the dots formed at pixel locations.
Producing dots of different sizes requires providing to the drive elements of the print head drive signals of complex waveforms. In actual practice, it is difficult to generate drive signals having appropriate waveforms for producing dots of the desired size. Even where a printing device uses only one dot size, it is difficult in certain instances to generate a drive signal having an appropriate waveform for producing dots of the proper size.
Further, in order to increase the printable area of a print medium, printing is sometimes performed using a different printing scheme for the top edge and bottom edge portions of the medium than is used in the medial area of the print medium. In such cases, the printing scheme employed for the top edge and bottom edge portion of the medium will ideally be conformable to the printing scheme employed for the medial area of the print medium.
Accordingly, an object of the present invention is to perform printing with drive signals having appropriate waveforms for producing dots of the desired size.
Another object of the present invention is to perform printing in the top edge and bottom edge portions of a print medium by means of a printing scheme that is conformable to the printing scheme employed for the medial area of the print medium.
In a printing apparatus according to the present invention, a maskable drive signal generator selectively generates for each main scan pass any of n types of maskable drive signals where n is an integer equal to 2 or greater. A drive signal masking section generates the drive signal to be supplied to ink-expulsion drive elements of a print head, by means of masking the maskable drive signal according to the print signal on a per-pixel basis. A controller of the printing apparatus executes printing, on at least a part of the print medium, according to a specific printing scheme wherein printing ink dots on each raster line is completed in nxc3x97m main scan passes while employing each of the n types of maskable drive signals m times on each raster line where m is an integer equal to 1 or greater.
In many instances, different maskable drive signals produce different print characteristics. Specifically, certain maskable drive signals can produce dots suitable for higher resolutions, while certain other maskable drive signals can produce dots suitable for higher speeds. Accordingly, where printing is carried out by means of n types of maskable drive signals, printing is accomplished with characteristics representing a combination of the characteristics of each maskable drive signal.
In one embodiment, at least one of the n types of maskable drive signals can effect printing at a print resolution different from that produced by other maskable drive signals when used alone for printing; and when a printing operation is performed using the n types of maskable drive signals, the printing of ink dots and the sub-scan feed are carried at in units of pixel pitches conforming to a lowest print resolution of the print resolutions achievable by the respective n types of maskable drive signals.
In this way, it is possible to effect printing not only with dots of the lowest print resolution, but with dots of higher resolution (i.e., smaller dots) as well, thereby affording smoother tone reproduction.
In another aspect of the present invention, when conducting main scan passes using at least one specific maskable drive signal from among the n types of maskable drive signals, a main scan driver conducts the main scan at a speed different from that of main scan conducted using other maskable drive signals.
It is permissible for main scan passes employing different maskable drive signals to be conducted at different main scan speeds. By so doing, there is provided a greater degree of freedom during maskable drive signal generation, so that drive signals having appropriate waveforms for producing dots of the desired size may be generated easily.
In still another aspect of the present invention, the controller executes printing according to a first printing scheme in a medial section of a printable area of the print medium, while in at least one of a leading edge portion and trailing edge portion of the printable area, executes printing according to a second printing scheme whose amount of the sub-scan feed is smaller than in the first printing scheme. With respect to raster lines printed according to the first printing scheme alone, the controller completes printing in the nxc3x97m main scan passes employing each of the n types of maskable drive signals m times. With respect to raster lines printed according to both the first printing scheme and the second printing scheme, the controller selects the maskable drive signal for each main scan pass according to the second printing scheme such that at least nxc3x97m main scan passes are performed employing each of the n types of maskable drive signals at least m times on each of the raster lines.
It is frequently the case that different maskable drive signals have different print characteristics. Specifically, certain maskable drive signals produce dots at high resolution, while certain other maskable drive signals produce dots at high speed. Accordingly, where printing is carried out by means of n types of maskable drive signals, printing is accomplished with characteristics representing a combination of the characteristics of each maskable drive signal. According to this aspect of the present invention, main scanning of raster lines in the edge portions of the printing area is carried out nxc3x97m times, employing each of n types of maskable drive signals at least m times, whereby printing in the edge portions of the printing area may be accomplished with characteristics representing a combination of the characteristics of each maskable drive signal, just as in the medial area. That is, according to the present invention, it is possible to perform printing in the edge portions of a print medium by means of a printing scheme that is integrated with the specific printing scheme used in the medial section of the print medium.
In one embodiment, the print head is capable of producing a plurality of dot types of different size for at least one ink color on a print medium using the nozzles, and the print signal contains multiple bits per pixel so as to allow each pixel to be printed in multi tones. Each of the n types of maskable drive signals includes a plurality of pulses during each pixel interval, and the drive signal masking section masks the maskable drive signals responsive to the multiple-bit print signal.
The effect of the invention is particularly great in this cases because different maskable drive signals are particularly likely to be used with print heads that can produce dots of different sizes.
The printing apparatus may perform bidirectional printing where the printing of ink dots takes place in both forward and reverse passes. In this case, different maskable drive signals may be selected for the forward pass and the reverse pass of main scan. In addition or alternatively, one of the n types of maskable drive signals may be selected for each main scan pass; and the main scan driver may perform each main scan at a speed appropriate to the selected maskable drive signal.
In this way, generation of maskable drive signals and printing by means of the same are facilitated.
Included among the specific aspects of the invention are inter alia a printing apparatus and printing method, a computer program for performing the functions of this apparatus or method, a computer-readable medium for storing this computer program, and a data signal containing this computer program and embodied in a carrier wave.